Your comparison is unfair, because CoffeeScript and Go try to do vastly different things. Go is a fairly low level systems language, while CoffeeScript is as high level as it gets.

That said, what Go achieves with its syntax is remarkable, imho.

Consider this: How do you add another function (e.g. "close()") to your file class in CoffeeScript? By extending the existing class into a "MyFile" class? But then you have to make sure all your "File" instances are actually instances of "MyFile", so you can call your newly defined function on them.

In Go you just define the new function.